This hungry critter wants to take a bite out of Bethlehem's watershed.

This is the story of a "very hungry caterpillar," only this version isn't for kids.

The caterpillar in this story is the antagonist — a loathsome eating-machine that views the forest surrounding Bethlehem's reservoirs as a waterfront restaurant.

Instead of munching on 16 delicious foods as in the children's picture book, this invasive villain is dining on the leaves on valuable hardwood trees that the city's water agency hopes to protect as part of a conservation program.

"They defoliate the trees — the caterpillar eats the leaves. The trees don't grow, and it limits our ability to raise a good watershed forest," said Steve Repasch, executive director of the Bethlehem Authority that oversees the reservoirs.

In an effort to write a happy ending to its story, the authority last week started a $10,800 spraying program to stop the rampage before the gypsy moth caterpillars even hatch on 245 acres surrounding the reservoirs in Carbon County.

It's the first time the authority, which owns 23,570 acres in Monroe and Carbon counties, has sprayed in more than 20 years. The decision came after a forester stumbled on masses of gypsy moth eggs last year while inspecting a tree stand for a possible timber sale, and a subsequent survey unveiled a huge concentration of eggs — some 500 egg masses per acre — in certain sections of the watershed.

"Our results indicate that we can expect areas of significant to complete defoliation in 2015," according to the report by authority consultants Woodland Management Services of Pike County.

Robin Wildermuth, owner and president of Woodland, said it often takes more than one year of defoliation to kill a tree. But add another stressor — like a drought or severe frost damage — and those tiny caterpillars can take a big bite out of the forest.

"We don't want to roll the dice," Wildermuth said. "We want to protect this forest the best we can, and let nature take over from there."

Gypsy moths aren't native to the area. They were introduced to North America in 1869 in Medford, Mass., by a man attempting a silk-production experiment, and the infestation spread quickly to other states. The first gypsy moths in Pennsylvania were found in Lackawanna and Luzerne counties in 1932.

Since then the gypsy moth has become one of the most destructive forest pests in the state, and oak tree stands are especially vulnerable, according to the Pennsylvania Forestry Bureau. In mid-May, the caterpillars start to feed in the northern part of the state on 500 species, but they especially like oak, apple, sweet gum, basswood, birch, aspen and willow trees. Older larvae also like hemlock, pines, spruce and other conifers.

Last year, gypsy moths defoliated 214,972 acres across Pennsylvania, according to the bureau.

That has the authority, which has invested $453,000 in its forestry program over the last dozen years, a little nervous. The authority does environmental logging — aimed at opening up the forest floor so the trees can regenerate — that also brings in revenue. In the last eight years, the authority has netted $509,635 from logging, 38 percent of which was raised last year.

The land is also part of a voluntary carbon credits program in which corporate polluters pay the authority money for keeping carbon locked in trees. Too big of a tree loss could affect how much money the authority eventually gets. The authority got $65,000 in carbon revenue in 2013 and $106,000 last year.

But nature has kept the caterpillars in check. Certain fungus and viruses are natural gypsy moth killers. But it's a cyclical process. Last year, for example, the cold, dry spring created the right conditions for the fungus to thrive and blunted the spread of gypsy moths.

That's not the case, so far this spring.

"The weather we had is not conducive to the fungus, which is the main knockout punch to caterpillar infestations," said Terry Brady, spokesman for the Pennsylvania Department of Conservation and Natural Resources.

The state has targeted 26,433 acres for its suppression program in six northeastern counties: Carbon, Columbia, Northumberland, Pike, Schuylkill and Luzerne. The Lehigh Valley hasn't had much of a problem so far this year, Brady said.

But, he added, a scenic stroll in the woods can quickly change that, and holiday hikers this weekend should be vigilant. The little critters are accomplished stowaways. Gypsy moth caterpillars like to hitch a ride on pant cuffs and in cars on their way to sample new backyard buffets.